Expression System Of NELL Peptide

ABSTRACT

Recombinant NELL peptides and methods of preparing the same are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser. No. 12/700,630, filed Feb. 4, 2010, which, in turn, is a divisional application of U.S. application Ser. No. 11/601,529 filed Nov. 17, 2006, the teaching of which is incorporated herein by reference in its entirety. U.S. application Ser. No. 11/601,529 is a continuation-in-part of U.S. application Ser. No. 10/544,553, filed May 15, 2006, which is a U.S. National Phase of PCT application PCT/US2004/003808, filed on Feb. 9, 2004, the teachings of which are incorporated herein by reference in their entirety. U.S. application Ser. No. 11/601,529 is also a continuation-in-part of PCT/US2006/005473, filed on Feb. 16, 2006, the teachings of which are incorporated herein by reference in their entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under Grant No. DE000422 and DE014649 awarded by the National Institutes of Health. The Government of the United States of America has certain rights in this invention.

FIELD OF THE INVENTION

The invention generally relates to methods for the expression and purification of a NELL peptide or a related agent.

BACKGROUND OF THE INVENTION

Growth factors are substances, such as peptides, which affect the growth and differentiation of defined populations of cells in vivo or in vitro.

Bone formation occurs during development of long bones (endochondral bone formation) and flat bones (intramembranous bone formation). Further, bone formation occurs during bone remodeling which occurs continuously in adult life in order to preserve the integrity of the skeleton. Finally, bone formation occurs during bone repair, such as when bone wounds occur in a fracture or surgical situation, for example. While separate bone formation mechanisms are thought to be involved in the embryological development of long and flat bones and repair is thought to involve intramembranous bone formation.

Bone formation by either mechanism involves the activity of osteoblasts, which are regulated by growth factors. Osteoblasts are derived from a pool of marrow stromal cells (also known as mesenchymal stem cells; MSC). These cells are present in a variety of tissues and are prevalent in bone marrow stroma. MSC are pluripotent and can differentiate into a variety of cell types including osteoblasts, chondrocytes, fibroblasts, myocytes, and adipocytes. Growth factors are thought to impact osteogenic cell proliferation, differentiation and osteoblast mineralization, each of which impacts bone formation.

Autogenous bone has been used, such to repair bone in patients with craniosynostosis and cleft grafting, for example. Craniosynostosis (CS), the premature closure of cranial sutures, affects 1 in 3,000 infants and therefore is one of the most common human congenital craniofacial deformities. Premature suture closure results in cranial dimorphism, which can need surgical correction. Premature suture closure in human CS can occur by two possibly distinct processes: calvarial overgrowth and bony fusion. Recently, fibroblast growth factor 2 (FGF2) and fibroblast growth factor receptor 1(FGFR1) have been implicated in premature cranial suture fusion via CBFA1-mediated pathways (8). Missense mutation of CBFA1 is linked to cleidocranial dysplasia, manifested as delayed suture closure.

Autologous bone grafting procedures have been performed utilizing autogenous bone, such as from the iliac crest or calvaria. These donor sites are not without associated morbidity including pain, gait disturbance, thigh paresthesia for iliac crest donor sites, and infection, neurologic deficits, and hematomas for calvarial grafts. Further, donor sites can have limited volume and can contribute to increased surgical time and hospital stay.

Alloplastic grafting materials have also been utilized, and growth factors have been tested in animal models. For example, bFGF has shown potential for use in bone regeneration and repair. Another family of osteogenic growth factors have been described as bone morphogenic protein (BMP). Specifically, BMP-2 recombinant protein has been demonstrated to regenerate mandibular continuity defects and cleft palate defects with results equal to or better than autogenous particulate bone and marrow. BMPs and other osteogenic factors have been studied for use in clinical applications. However, the cost of using minimally effective dosages of BMP has been a limiting factor in clinical use.

Spinal fusion is a surgical technique in which one more of the vertebrae of the spine are united together so that motion no longer occurs between them. Indications include: treatment of a fractured (broken) vertebra, correction of deformity, elimination of pain from motion, treatment of instability, and treatment of some cervical disc herniations. The surgery can involve placement of a bone graft between the vertebrae to obtain a solid union between the vertebrae. The procedure also can involve supplemental treatments including the placement of plates, screws, cages, and recently bone morphogenic protein 2 and 7 to assist in stabilizing and healing the bone graft. Autogenous bone grafting has been the clinically preferred method, and yet has about a 30-50% failure rate. Autogenous bone grafting is a separate surgery and also carries significant morbidity.

Cartilage is a type of dense connective tissue. It is composed of chondrocytes which are dispersed in a firm gel-like matrix. Cartilage is avascular (contains no blood vessels) and nutrients are diffused through the matrix. Cartilage is found in the joints, the rib cage, the ear, the nose, in the throat and between intervertebral disks. There are three main types of cartilage: hyaline (e.g., costal cartilages, the cartilages of the nose, trachea, and bronchi, and the articular cartilages of joints), elastic (e.g., external ear, external auditory meatus, part of the Eustachian tube, epiglottis, and in some of the laryngeal cartilages) and fibrocartilage [e.g. meniscus (e.g., wrist triangular fibrocartilage complex, knee meniscus), intervertebral discs, temporomandibular joint disc, the pubic symphysis, and in some tendons and ligaments at their attachment to bones. One of the main purposes of cartilage is to provide a framework upon which bone deposition could begin (i.e., during endochondral ossification). Another important purpose of cartilage is to provide smooth surfaces for the movement of articulating bones. For example, articular cartilage, most notably that which is found in the knee joint, is generally characterized by very low friction, high wear resistance, and poor regenerative qualities. It is responsible for much of the compressive resistance and load bearing qualities of the knee joint and, without it, walking is painful to impossible. Yet another important purpose of cartilage is to provide, firm, yet flexible support (e.g., nasal cartilage, spinal discs, tracheal cartilage, knee meniscus, bronchial cartilage). For instance, cartilage such as the meniscus plays a crucial role in joint stability, lubrication, and force transmission. Under a weight bearing load, the meniscus maintains the balanced position of the femur on the tibia and distributes the compressive forces by increasing the surface contact area, thereby decreasing the average stress two to three times. Additionally, the menisci interact with the joint fluid to produce a coefficient of friction that is five times as slick as ice on ice. In another example, the intervertebral disc has several important functions, including functioning as a spacer, as a shock absorber, and as a motion unit. The gelatinous central portion of the disc is called the nucleus pulposus. It is composed of 80-90% water. The solid portion of the nucleus is Type II collagen and non-aggregated proteoglycans. The outer ligamentous ring around the nucleus pulposus is called the annulus fibrosus, which hydraulically seals the nucleus, and allows intradiscal pressures to rise as the disc is loaded. The annulus has overlapping radial bands, not unlike the plies of a radial tire, and this allows torsional stresses to be distributed through the annulus under normal loading without rupture. The disc functions as a hydraulic cylinder. The annulus interacts with the nucleus. As the nucleus is pressurized, the annular fibers serve a containment function to prevent the nucleus from bulging or herniating.

Cartilage can be damaged by wear, injury or diseases. As we age, the water and protein content of the body's cartilage changes. This change results in weaker, more fragile and thin cartilage. Osteoarthritis is a common condition of cartilage failure that can lead to limited range of motion, bone damage and invariably, pain. Due to a combination of acute stress and chronic fatigue, osteoarthritis directly manifests itself in a wearing away of the articulating surface and, in extreme cases, bone can be exposed in the joint. In another example, loss of the protective stabilizing meniscus leads to increased joint laxity or abnormal motions that lead to joint instability. The excessive motion and narrowed contact area promotes early arthritic changes. At the cellular level, there is initially a loss of cells from the superficial layer of the articular cartilage followed by cartilage splitting, subsequent thinning and erosion occurs, and finally protrusion of the underlying raw bone. The earliest arthritic changes have been noted three weeks after loss of the entire meniscus. In yet another example, because both the discs and the joints that stack the vertebrae (facet joints) are partly composed of cartilage, these areas are subject to wear and tear over time (degenerative changes). As the inner nucleus dehydrates, the disc space narrows, and redundant annular ligaments bulge. With progressive nuclear dehydration, the annular fibers can crack and tear. Loss of normal soft tissue tension may allow the spinal segment to sublux (e.g. partial dislocation of the joint), leading to osteophyte formation (bone spurs), for aminal narrowing, mechanical instability, and pain. If the annular fibers stretch or rupture, allowing the pressurized nuclear material to bulge or herniate and compress neural tissues, pain and weakness may result. This is the condition called a pinched nerve, slipped disc, or herniated disc. Radiculopathy refers to nerve irritation caused by damage to the disc between the vertebrae. Mechanical dysfunction may also cause disc degeneration and pain (e.g. degenerative disc disease). For example, the disc may be damaged as the result of some trauma that overloads the capacity of the disc to withstand increased forces passing through it, and inner or outer portions of the annular fibers may tear. These torn fibers may be the focus for inflammatory response when they are subjected to increased stress, and may cause pain directly, or through the compensatory protective spasm of the deep paraspinal muscles.

There are several different repair options available for cartilage damage or failure.

Osteoarthritis is the second leading cause of disability in the elderly population in the United States. It is a degenerative disorder that generally starts off relatively mild and escalates with time and wear. For those patients experiencing mild to moderate symptoms, the disorder can be dealt with by several non-surgical treatments. The use of braces and drug therapies, such as anti-inflammatories (ex. diclofenac, ibuprofen, and naproxen), COX-2 selective inhibitors, hydrocortisone, glucosamine, and chondroitin sulfate, have been shown to alleviate the pain caused by cartilage deficiency and some claim they can slow the degenerative process.

Most surgical treatments for articular cartilage, short of total joint replacement, can be divided into various treatment groups. Treatments that remove the diseased and undermined cartilage with an aim to stop inflammation and pain include shaving (chondrectomy) and debridement. Another group of treatments consists of a range of abrasive procedures aimed at triggering cartilage production, such as drilling, microfracture surgery, chondroplasty, and spongialization. Abrasion, drilling, and microfracture originated 20 years ago. They rely on the phenomenon of spontaneous repair of the cartilage tissue following vascular injury to the subchondral plate of the bone. Laser assisted treatments, currently experimental, compose another category; they combine the removal of diseased cartilage with cartilage reshaping and also induce cartilage proliferation. Additional treatments include autologous cartilage implants (e.g., Carticel by Genzyme).

Other treatments that can be more applicable to meniscal cartilage include early surgical intervention and suture repair of torn structures or allograft meniscus transplantation in severe injury cases.

Although the overwhelming majority of patients with a herniated disc and sciatica heal without surgery, if surgery is indicated procedures include removal of the herniated disc with laminotomy (producing a small hole in the bone of the spine surrounding the spinal cord), laminectomy (removal of the bony wall adjacent to the nerve tissues), by needle technique through the skin (percutaneous discectomy), disc-dissolving procedures (chemonucleolysis), and others. For patients with mechanical pain syndrome, unresponsive to conservative treatment, and disabling to the individual's way of life, the problem can be addressed by spinal fusion, intradiscal electrothermal coagulation (or annuloplasty), posterior dynamic stabilization, artificial disc technologies, or still experimental disc regeneration therapies using various molecular based therapies delivered using proteins, peptides, gene therapies, or nucleotides. Although numerous methods have been described for treatment of cartilage problems, it is clear that many are artificial or mechanically based solutions that do not seek to recreate normal cartilage tissue biology. Therefore, there is a need for methods for stimulating cartilage formation.

Therefore, there is a need for compositions and methods to induce bone formation in bone development, disorders, or bone trauma.

Therefore, there is a need for compositions and methods to induce cartilage formation and regeneration.

SUMMARY OF THE INVENTION

The present invention is related to methods for the expression and purification of NELL1 and NELL2 proteins. The method includes:

providing a nucleic acid construct including at least a nucleic acid encoding at least a NELL peptide in frame with a nucleic acid encoding a secretory signal peptide;

transfecting a mammalian cell with said nucleic acid construct; and

culturing said mammalian cell under conditions that permit expression of the NELL peptide.

In some embodiments, the mammalian cell is a Chinese hamster ovary cell. The method can further include collecting NELL peptide secreted from the cell line; and substantially purifying the NELL peptide. In some embodiments, the method can further include testing the activity of the NELL peptide to induce bone formation.

The NELL protein produced by the expression system described herein can be used alone or with other agents for bone or cartilage formation or regeneration.

In some embodiments, the NELL protein described herein can be used to form a composition in any desirable formulation. Some examples of NELL protein compositions and formulations are described in U.S. patent Ser. No. 11/392,294, and PCT/US2006/005473, the teachings of which are incorporated hereto by reference in their entirety. In some embodiments, the composition or formulation can include a carrier, e.g., a pharmaceutically acceptable carrier. In some embodiments, a substrate can include cells and/or NELL1 peptide which can facilitate bone cartilage, disc, or other forms of tissue repair in the proximity of the implant.

In some embodiments, the invention includes methods of inducing osteogenic differentiation, osteoblastic mineralization and/or bone formation in a variety of clinical applications. The invention also includes methods of inducing chondrogenic differentiation and/or chondrogenic mineralization in a variety of clinical applications.

In some embodiments, this invention can provide a greater effect than known growth factors and/or can enhance the activity of other growth factors. Therefore, lower doses of each growth factor can be used for clinical applications. This is significant at least in that clinical treatments can be more affordable. Further this invention is advantageous at least in that NELL1 enhances osteogenic differentiation, osteoblastic mineralization and bone formation, which can improve the clinical rate and effectiveness of treatment with BMPs alone. This invention is also advantageous in that NELL1 enhances chondrogenic differentiation and/or chondrogenic mineralization which can improve the clinical rate and effectiveness of treatment with BMP alone.

Some examples of NELL protein compositions and formulations are described in U.S. patent Ser. No. 11/392,294, and PCT/US2006/005473, the teachings of which are incorporated hereto by reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B show a flow diagram of one method of producing a NELL peptide.

FIGS. 2A-2D illustrate a signal peptide-NELL1-FLAG nucleic acid construct (SEQ ID NO:15). Underlined amino acid sequences are derived from melittin signal peptide. The bond between Alanine and Proline is a putative cleavage site for secretion by High Five cells. The residues from RTVLGFG (Residues 38-44 of SEQ ID NO:16)—are derived from the mature protein of rat/human NELL1 protein.

FIGS. 3A-3D illustrate the products of extracellular expression of NELL1-FLAG FIG. 3A is a CBB-stained SDS-PAGE gel of UnoQ-eluate containing purified NELL1 peptide produced from high five cells in serum-free medium (Productivity: ca. 3 mg/L medium); FIG. 3B is a Western blotting using anti-FLAG antibody. FIG. 3C is a CBB-stained SDS-PAGE gel of UnoQ-eluate containing purified NELL1 peptide produced from COS7 cells in serum-free medium (Productivity: <0.1 mg/L medium). FIG. 3D is a Western blotting using anti-FLAG antibody.

FIGS. 4A-4C illustrate the production of NELL1 peptide (SEQ ID NO:2) by a CHO expression system. FIG. 4A is the depiction of the nucleic acid sequence of the cDNA construct used in this example and amino acid sequences of three different signal peptides (residues 1-16 of SEQ ID NO:2, residues 1-21 of SEQ ID NO:8, and SEQ ID NO:17, respectively). FIG. 4B is a Western blot with anti-c-myc antibody detecting secreting NELL1 from transfections with different constructs after immunoprecipitation using anti-c-myc agarose. FIG. 4C is a Western blot with anti-c-myc or mouse anti-human NELL1 antibodies detecting secreting NELL1 after immunoprecipitation using rabbit anti-human Nell-1 antibody-NHS activated sepharose.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to methods for the expression and purification of NELL1 and NELL2 proteins. The method includes:

providing a nucleic acid construct including at least a nucleic acid encoding at least a NELL peptide in frame with a nucleic acid encoding a secretory signal peptide;

transfecting a mammalian cell with said nucleic acid construct; and

culturing said mammalian cell under conditions that permit expression of the NELL peptide.

In some embodiments, the mammalian cell is a Chinese hamster ovary cell. The method can further include collecting NELL peptide secreted from the cell line; and substantially purifying the NELL peptide. In some embodiments, the method can further include testing the activity of the NELL peptide to induce bone formation.

The NELL protein produced by the expression system described herein can be used alone or with other agents for bone or cartilage formation or regeneration. In some embodiments, the NELL protein described herein can be used to form a composition in any desirable formulation. In some embodiments, the composition or formulation can include a carrier, e.g., a pharmaceutically acceptable carrier. In some embodiments, a substrate can include cells and/or NELL1 peptide which can facilitate bone cartilage, disc, or other forms of tissue repair in the proximity of the implant.

In some embodiments, the invention includes methods of inducing osteogenic differentiation, osteoblastic mineralization and/or bone formation in a variety of clinical applications. The invention also includes methods of inducing chondrogenic differentiation and/or condrogenic mineralization in a variety of clinical applications.

In some embodiments, this invention can provide a greater effect than known growth factors and/or can enhance the activity of other growth factors. Therefore, lower doses of each growth factor can be used for clinical applications. This is significant at least in that clinical treatments can be more affordable. Further this invention is advantageous at least in that NELL1 enhances osteogenic differentiation, osteoblastic mineralization and bone formation, which can improve the clinical rate and effectiveness of treatment with BMPs alone. This invention is also advantageous in that NELL1 enhances chondrogenic differentiation and/or chondrogenic mineralization which can improve the clinical rate and effectiveness of treatment with BMP alone.

Some examples of NELL protein compositions and formulations are described in U.S. patent Ser. No. 11/392,294, and PCT/US2006/005473, the teachings of which are incorporated hereto by reference in their entirety.

DEFINITION

The terms “polypeptide”, “peptide” and “protein” can be used interchangeably herein to refer to a polymer of amino acid residues. The terms can apply to amino acid polymers in which one or more amino acid residue is an artificial chemical analogue of a corresponding naturally occurring amino acid, as well as to naturally occurring amino acid polymers.

The term “antibody” can include various forms of modified or altered antibodies, such as an intact immunoglobulin, an Fv fragment containing only the light and heavy chain variable regions, an Fv fragment linked by a disulfide bond, a Fab or (Fab)′2 fragment containing the variable regions and parts of the constant regions, a single-chain antibody and the like. An antibody can include intact molecules as well as fragments thereof, such as, Fab and F(ab′)^(2′), and/or single-chain antibodies (e.g. scFv) which can bind an epitopic determinant. An antibody can be of animal (such as mouse or rat) or human origin or can be chimeric or humanized. Antibodies can be polyclonal or monoclonal antibodies (“mAb's”), such as monoclonal antibodies with specificity for a polypeptide encoded by a NELL1 or NELL 2 protein.

The term “capture agent” can refer to molecules that specifically bind other molecules to form a binding complex such as antibody-antigen, lectin-carbohydrate, nucleic acid-nucleic acid, biotin-avidin, and the like.

The term “specifically binds” can refer to a biomolecule (e.g., protein, nucleic acid, antibody, etc.), refers to a binding reaction which is determinative of the presence biomolecule in heterogeneous population of molecules (e.g., proteins and other biologics). Thus, under designated conditions (e.g. immunoassay conditions in the case of an antibody or stringent hybridization conditions in the case of a nucleic acid), the specified ligand or antibody can bind to its particular “target” molecule and can not bind in a significant amount to other molecules present in the sample.

The terms “nucleic acid” or “oligonucleotide” can refer to at least two nucleotides covalently linked together. A nucleic acid of the present invention can be single-stranded or double stranded and can contain phosphodiester bonds, although in some cases, nucleic acid analogs can be included that can have alternate backbones, comprising, for example, phosphoramide, phosphorothioate, phosphorodithioate, omethylphophoroamidite linkages, and/or peptide nucleic acid backbones and linkages. Analog nucleic acids can have positive backbones and/or non-ribose backbones. Nucleic acids can also include one or more carbocyclic sugars. Modifications of the ribose-phosphate backbone can be done to facilitate the addition of additional moieties such as labels, or to increase the stability and half-life of such molecules in physiological environments, for example.

The term “specific hybridization” can refer to the binding, duplexing, or hybridizing of a nucleic acid molecule preferentially to a particular nucleotide sequence under stringent conditions, including conditions under which a probe can hybridize preferentially to its target subsequence, and can hybridize to a lesser extent to other sequences.

The terms “NELL1 cDNA” refer to SEQ ID NO:1, 3 and 5, and “NELL2 cDNA” can refer to SEQ ID NO:7, 9, 11 and 13.

NELL Peptides

NELL1 is a 810 aa (amino acid) peptide, distributed primarily in bone. In adults, NELL1 is expressed at high levels in craniofacial bone, and lower levels in long bone. Its role in osteoblast differentiation, bone formation and regeneration has been examined NELL 2 is a 816 aa peptide, distributed in neural cells and brain.

Human NELL1 gene includes at least 3 Cbfa1 response elements in the promoter region. Cbfa1 specifically binds to these response elements in the NELL1 promoter. NELL1 expression can be under the control of this transcription factors expressed endogenously at least in preosteoblasts, osteoblasts and hypertrophic chondrocytes in development and in adulthood. Cleidocranial disostosis is a developmental cranial defect thought to be caused at least in part by Cbfa disruption.

A NELL1 peptide is a protein which can be expressed by the NELL1 gene or cDNA and includes SEQ ID NO: 2, 4, and 6. The NELL1 peptide can include a NELL1 peptide fragment that retains the ability to induce osteogenic cell differentiation, osteoblast differentiation or bone formation. A NELL2 peptide is a protein which can be expressed by the NELL2 gene or cDNA and includes SEQ ID NO: 8, 10, 12 and 14. The NELL2 peptide can include NELL2 peptide fragments that retain similar activity to the full NELL2 peptide sequence.

The term “derivative” as used herein, refers to any chemical or biological compounds or materials derived from a NELL peptide, structural equivalents thereof, or conformational equivalents thereof. For example, such a derivative can include any pro-drug form, PEGylated form, or any other form of a NELL peptide that renders the NELL peptide more stable or to have a better osteophilicity or lipophilicity. In some embodiments, the derivative can be a NELL peptide attached to poly(ethylene glycol), a poly(amino acid), a hydrocarbyl short chain having C1-C20 carbons, or a biocompatible polymer. In some embodiments, the term “derivative” can include a NELL peptide mimetics. As used herein, the term “mimetic” refers to a peptide having at least one non-peptide bond in its backbone. A peptide bond is a chemical bond formed between the carboxylic acid group of an amino acid molecule and the amino group of another amino acid molecule.

Synthesis of mimetics of a peptide is well document in the art. The following describes an example of the basic procedure for the synthesis of a peptide, including a peptide mimetics:

Before the peptide synthesis starts, the amine terminus of the amino acid (starting material) can protected with FMOC (9-fluoromethyl carbamate) or other protective groups, and a solid support such as a Merrifield resin (free amines) is used as an initiator. Then, step (1) through step (3) reactions are performed and repeated until the desired peptide is obtained: (1) a free-amine is reacted with carboxyl terminus using carbodiimide chemistry, (2) the amino acid sequence is purified, and (3) the protecting group, e.g., the FMOC protecting group, is removed under mildly acidic conditions to yield a free amine. The peptide can then be cleaved from the resin to yield a free standing peptide or peptide mimetics.

In one embodiment, the method can include providing a nucleic acid sequence encoding a NELL peptide, such as NELL1 or NELL2 peptide, in frame with a nucleic acid sequence encoding a secretory signal peptide. In one embodiment, the secretory signal peptide can be a secretory signal peptide from a secreted bee protein. For example, the nucleic acid sequence can be selected from the group including, but not limited to a melittin signal sequence, drosphila immunoglobulin-binding protein signal sequence, equine interferon-gamma (eIFN-gamma) signal peptide, snake phospholipase A2 inhibitor signal peptide, human and/or chicken lysozyme signal peptide. For mammalian expression systems, a protrypsin leading sequence can also be used.

In one embodiment, the method can include transfecting an insect cell line with a nucleic acid construct encoding a NELL peptide; and culturing the insect cell line under conditions that permit expression and/or secretion of the NELL peptide. For example, the cell line can be transfected transiently or stably with the nucleic acid construct encoding a NELL peptide.

Systems Expressing NELL Peptides

A NELL peptide can be expressed in any biological system. For example, a NELL peptide can be expressed in a bacterial system, a yeast system, a plant system, or animal system.

In some embodiments, a NELL peptide can be expressed in a cell free expression system well known to those in the art. For example, E coli cell-free protein translation systems or wheat germ cell-free protein translation systems.

In some embodiments, a NELL peptide can be expressed in transgenic plant cell systems derived from tobacco, corn, rice, or soybean.

Such expression systems can include a carrier such as a viral carrier or viral vector, peptide carrier, or a short polymer molecule.

In some embodiments, a NELL peptide can be expressed in insect cells. The NELL1 and NELL2 peptides expressed in an insect system are functional forms of the protein.

COS7 cells can be used to produce NELL1 and NELL2 proteins at low levels, such as about 10 micrograms per litter medium, but require serum-containing medium for the expression. As for the signal peptides, NELL1 and NELL2 endogenous signal peptides permit expression in COS7 cells.

In one embodiment, the invention includes a method of expressing a functional NELL peptide, such as NELL1 or NELL2 peptide, using an insect cell line. In one embodiment, the insect cell can be a high five cell, Sf9 and other Sf cells.

In one embodiment, the method can include providing a nucleic acid sequence encoding a NELL peptide, such as NELL1 or NELL2 peptide. The nucleic acid sequence can be a cDNA or genomic DNA, encoding at least a functional portion of a NELL peptide. For example, the nucleic acid sequence can be selected from the group including, but not limited to human NELL1 (SEQ ID NO:1), rat NELL1 (SEQ ID NO:3), mouse NELL1 (SEQ ID NO:5), or human NELL2 (SEQ ID NO:7), rat NELL2 (SEQ ID NO:9), mouse NELL2 (SEQ ID NO:11), chicken NELL2 (SEQ ID NO:13). The nucleic acid sequence can also include sequences such as those with substantial sequence similarity, such as sequences having at least about 75% sequence similarity with any portion of the sequences listed above.

Further the nucleic acid can include an expression vector for expressing the nucleic acid sequence encoding a NELL peptide, such as NELL1 or NELL2 peptide. For example, the expression vector can be pIZT/V5-His (Invitrogen), and selective markers can also include blastcidin and neomycin.

Further, the nucleic acid sequence can also include additional nucleic acids which encode reporter products to monitor levels of gene expression, or encode peptide tags which can be visualized using known methods in the art to monitor levels of peptide expression. Additional sequences can be selected so as to not interfere with the expression of the nucleic acid, or the functionality of the expressed peptide product.

In one embodiment, the invention can include a nucleic acid construct for expressing a NELL peptide, such as NELL1 and/or NELL2 peptide in an insect cell. The nucleic acid sequence can be a cDNA or genomic DNA, encoding at least a functional portion of a NELL peptide. For example, the nucleic acid sequence can be selected from the group including, but not limited to human NELL1 (SEQ ID NO:1), rat NELL1 (SEQ ID NO:3), mouse NELL1 (SEQ ID NO:5), or human NELL2 (SEQ ID NO:7), rat NELL2 (SEQ ID NO:9), mouse NELL2 (SEQ ID NO:11), chicken NELL2 (SEQ ID NO:13). The nucleic acid sequence can also include sequences such as those with substantial sequence similarity, such as sequences having at least about 75% sequence similarity with any portion of the sequences listed above.

In one embodiment, the invention can include a nucleic acid construct for expressing a NELL peptide, such as NELL1 and/or NELL2 peptide in a mammalian cell such as a Chinese hamster ovary cell (CHO cell). The nucleic acid sequence can be a cDNA or genomic DNA, encoding at least a functional portion of a NELL peptide. For example, the nucleic acid sequence can be selected from the group including, but not limited to human NELL1 (SEQ ID NO:1), rat NELL1 (SEQ ID NO:3), mouse NELL1 (SEQ ID NO:5), or human NELL2 (SEQ ID NO:7), rat NELL2 (SEQ ID NO:9), mouse NELL2 (SEQ ID NO:11), chicken NELL2 (SEQ ID NO:13). The nucleic acid sequence can also include sequences such as those with substantial sequence similarity, such as sequences having at least about 75% sequence similarity with any portion of the sequences listed above.

In some embodiments, for production of NELL1 and/or NELL2 peptides in mammalian cells (e.g., CHO cells), the expressing system for NELL1 and/or NELL2 can include the nucleic acid or cDNA that expresses the endogenous signal peptide. In some embodiments, the expressing system for NELL1 and/or NELL2 peptides can include the nucleic acid or cDNA that expresses NELL2 signal peptide. The incorporation of the NELL2 signal nucleic acid or cDNA into the system expressing NELL1 peptide allows the production of the NELL1 peptide more efficiently.

The nucleic acid construct can include a nucleic acid sequence encoding a signal peptide. The nucleic acid can include an expression vector for expressing the nucleic acid sequence encoding a NELL peptide. Further, the nucleic acid sequence can include additional nucleic acids which encode reporter products to monitor levels of gene expression, or encode peptide tags which can be visualized using known methods in the art to monitor levels of peptide expression.

Nucleic acid constructs can comprise expression and cloning vectors should containing a selection gene, also termed a selectable marker, such as a gene that encodes a protein necessary for the survival or growth of a host cell transformed with the vector. The presence of this gene ensures that any host cell which deletes the vector will not obtain an advantage in growth or reproduction over transformed hosts. Typical selection genes encode proteins that (a) confer resistance to antibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate or tetracycline, (b) complement auxotrophic deficiencies.

Nucleic acid constructs can also include a promoter which is recognized by the host organism and is operably linked to the NELL encoding nucleic acid. Promoters are untranslated sequences located upstream from the start codon of a structural gene (generally within about 100 to 1000 bp) that control the transcription and translation of nucleic acid under their control, including inducible and constitutive promoters. Inducible promoters are promoters that initiate increased levels of transcription from DNA under their control in response to some change in culture conditions, e.g. the presence or absence of a nutrient or a change in temperature. At this time a large number of promoters recognized by a variety of potential host cells are well known.

A nucleic acid can be operably linked when it is placed into a functional relationship with another nucleic acid sequence. For example, DNA for a presequence or secretory leader is operably linked to DNA for a polypeptide if it is expressed as a preprotein which participates in the secretion of the polypeptide; a promoter or enhancer is operably linked to a coding sequence if it affects the transcription of the sequence; or a ribosome binding site is operably linked to a coding sequence if it is positioned so as to facilitate translation.

In one embodiment, the invention can include cells that express functional NELL peptides. For example, the cell can be a CHO cell. In one embodiment, the cell can be transfected with a nucleic acid construct encoding a NELL peptide. For example, the cell line can be transfected transiently or stably with the nucleic acid construct encoding a NELL peptide. In one embodiment, NELL expressing nucleic acids (e.g., cDNA(s) can be cloned into gene expression vector or viral particles that are competent to transfect cells (such as insect cells or Chinese hamster ovary cells (CHO cells)).

The nucleic acid sequence can also include a nucleic acid sequence encoding a NELL peptide, such as NELL1 or NELL2 peptide, in frame with a nucleic acid sequence encoding an insect secretory signal peptide.

In one embodiment, the invention can include cells that express functional NELL peptides, and can secrete functional proteins.

In one embodiment, the invention can include a polypeptide (amino acid sequence) comprising a NELL peptide, such as NELL1 or NELL2 peptide, and can include secretory signal peptide.

For example, the amino acid sequence of the NELL peptide can be selected from the group including, but not limited to human NELL1 (SEQ ID NO:2), rat NELL1 (SEQ ID NO:4), mouse NELL1 (SEQ ID NO:6), or human NELL2 (SEQ ID NO:8), rat NELL2 (SEQ ID NO:10), mouse NELL2 (SEQ ID NO:12), chicken NELL2 (SEQ ID NO:14). The amino acid sequence can also include sequences such as those with substantial similarity, such as sequences having at least about 75% sequence similarity with any portion of the sequences listed above, or contain similar active binding domains as NELL1 peptides.

Peptide Purification

In some embodiments, the invention includes a method purifying NELL1 and/or NELL2 peptides secreted into culture media, according to standard peptide purification protocols, including, but not limited to those described below.

The method can also include collecting secreted NELL peptides and/or purifying NELL peptides for use. Peptide products can be tested for activity in a variety of functional or expression assays. For example in any assay, if a NELL peptide has a significant effect over a control substance on a given parameter, the NELL peptides can be said to be functional to effect the measured parameter.

In one embodiment, whether a selected cell expresses a selected nucleic acid sequence to express and/or secrete a NELL peptide can be examined. In one embodiment, the presence, amount or and/or activity of NELL peptides can be examined.

In on embodiment, NELL peptides detected and quantified by any of a number of methods well known to those of skill in the art. These can include analytic biochemical methods such as electrophoresis, capillary electrophoresis, high performance liquid chromatography (HPLC), thin layer chromatography (TLC), hyperdiffusion chromatography, and the like, or various immunological methods such as fluid or gel precipitin reactions, immunodiffusion (single or double), immunoelectrophoresis, radioimmunoassay (RIA), enzyme-linked immunosorbent assays (ELISAs), immunofluorescent assays, western blotting, and the like.

In one embodiment, Western blot (immunoblot) analysis can be used to detect and quantify the presence of NELL peptide(s) in a selected sample. This technique can include separating sample proteins by gel electrophoresis on the basis of molecular weight, transferring the separated proteins to a suitable solid support, (such as a nitrocellulose filter, a nylon filter, or derivatized nylon filter), and incubating the sample with the antibodies that specifically bind a target peptide.

The assays of this invention can be scored (as positive or negative or quantity of target polypeptide) according to standard methods well known to those of skill in the art. The particular method of scoring can depend on the assay format and choice of label. For example, a Western Blot assay can be scored by visualizing the colored product produced by an enzymatic label. A clearly visible colored band or spot at the correct molecular weight can be scored as a positive result, while the absence of a clearly visible spot or band can be scored as a negative. The intensity of the band or spot can provide a quantitative measure of target polypeptide concentration.

EXAMPLES

Methods for recombinant protein production and purification are well known to those in the art with several commercial company offering protein production services. The following examples are offered to illustrate, but not to limit the claimed invention. In general expression hosts can be: bacteria, yeast and fungi, mammalian cells, plants, transgenic animals (e.g., goat milk) or it can also be cell-free expression systems such as those based on wheat germ or E. coli extracts. In general, expression elements can be Prokaryotic, Yeast, Mammalian and Plant promoters or viral promoters. Protein expression strategies can be: intra- or extracellular, fusion proteins and display strategies. Downstream processing of recombinant proteins can include: harvest, lysis, filtration, ultrafiltration, precipitation, and/or other protein processing/purification strategies that encompass protein capture, purification, polishing, and optimization.

Example 1 Expression of NELL Peptides

A cDNA fragment was ligated into the expression vector PiZT/V5-His (3.4 kb) (EcoRV site, Invitrogen) and included a melittin signal peptide, BamHI-EcoRI cDNA fragment of the mature rat NELL1 and a FLAG tag sequence. FIGS. 2A-2B are a depiction of the nucleic acid sequence of the cDNA construct used in this example, and corresponding predicted peptide sequence.

The High five cells (BTI-TN-5B1-4) were adapted to serum-free medium, and cells were transfected with the NELL1 peptide expression vector. Cells were treated with zeocin so as to select only cell populations expressing the NELL1 FLAG constructs. Surviving cell populations were confirmed to be stable transformants. Extracellular media was collected and tested for the presence of NELL1 peptide. NELL1 peptide was purified and used in functional assays described below.

FIG. 2A is an illustration of a CBB-stained SDS-PAGE gel of UnoQ-eluate containing purified NELL1 peptide. The medium was applied onto UnoQ column (Bio-Rad) as described herein. FIG. 2B shows a Western blot using anti-FLAG antibody depicting NELL1-FLAG expression in reference to a protein ladder. Peptide: 140 kDa (intracellular precursor), 130 kDa (mature form; 90 kDa peptide), 400 kDa (secreted form, homotrimer). In the example above, the productivity of the expression system was about 3 mg NELL1 peptide/L medium.

Relative to other expression systems which did not express or secrete peptide at all (such as bacterial expression, including yeast) or whose peptide production was extremely low (e.g., E. coli fused peptide system, CHO-dhfr cells, >10 mcg/L) production with the systems described (mammalian and insect cells) was surprisingly and substantially more effective at producing large amounts of functional protein.

Expression and Purification of Recombinant Rat NELL1 Protein. For production of the C-terminally FLAG-tagged NELL1 peptide by insect cells, a pIZT-NELL1-FLC plasmid was constructed by inserting the rat NELL1 cDNA fused to a FLAG epitope sequence derived from the pTB701-NELL1-FLC plasmid (Kuroda, BBRC) into insect expression vector pIZT/V5-His (Invitrogen). Furthermore, NELL1 original secretory signal sequence was replaced to honeybee mellitin signal sequence using PCR methods. High Five cells were purchased from Invitrogen, and were cultured in High Five Serum-Free Medium (Invitrogen). High Five cells were transfected with the pIZT-NELL1-FLC plasmid using FuGene6 (Roche). Forty-eight hours after transfection, cells were selected with 400 mg/ml of Zeocin (Invitrogen). Replace selective medium every 3 to 4 days until the stable expression cell line was established. NELL1 secretion was confirmed using immunoprecipitation and Western blot analyses. High five cells were found to express NELL1 peptides (140-kDa) in the culture medium.

The recombinant rat NELL1-FLC peptide was purified from the culture medium of Zeocin-resistant High Five cells by anion exchange chromatography using a UNO Q-1 column (Bio-Rad). NELL1 peptide was eluted at 500 mM NaCl.

For production of the C-terminally FLAG-tagged NELL1 peptide by COS7 cells, a pcDNA3.1-NELL1-FLC plasmid was constructed by inserting the rat NELL1 cDNA linked to a FLAG epitope sequence derived from the pTB701-NELL1-FLC plasmid into mammalian expression vector pcDNA3.1 (Invitrogen). COS7 cells were cultured in DMEM supplemented with 10% FBS. COS7 cells were transfected with the pcDNA3.1-NELL1-FLC using the endogenous NELL signal peptide plasmid and using electroporation method. Forty-eight hours after transfection, culture medium was subjected to immunoprecipitation and Western blot analyses for NELL1 peptide.

FIG. 3C is an illustration of a CBB-stained SDS-PAGE gel of UnoQ-eluate. including NELL1-FLAG. These expression studies showed that COS cells did not express functional NELL peptide, without modifying the N terminal of the NELL to increase secretion efficiency such as including a signal sequence. FIG. 3D is an illustration of a Western blot using anti-FLAG antibody depicting NELL1-FLAG expression.

Expression and Purification of Recombinant Rat NELL2 Protein. For production of the C-terminally FLAG-tagged NELL2 peptide by insect cells, a pIZT-NELL1-FLC plasmid was constructed by inserting the rat NELL2 cDNA fused to a FLAG epitope sequence derived from the pTB701-NELL2-FLC plasmid into insect expression vector pIZT/V5-His (Invitrogen). High Five cells were purchased from Invitrogen, and were cultured in High Five Serum-Free Medium (Invitrogen). High Five cells were transfected with the pIZT-NELL1-FLC plasmid using FuGene6 (Roche). Forty-eight hours after transfection, cells were selected with 400 mg/ml of Zeocin (Invitrogen). Selective media was replaced every 3 to 4 days, until the stable expression cell line was established. NELL2 expression was confirmed in culture medium was confirmed using immunoprecipitation and Western blot analyses. High five cells were found to express NELL2 peptides (140-kDa) in the culture medium.

The recombinant rat NELL2-FLC peptide was purified from the culture medium of Zeocin-resistant High Five cells by anion exchange chromatography using a UNO Q-1 column (Bio-Rad). NELL2-FLC peptide was eluted at 500 mM NaCl.

Example 2 Expression of NELL1 in Mammalian Systems

The mammalian expression system used for production of rhNELL1 by non-viral DNA delivery in this invention may include, but not limit to these commonly used stable suspension systems listed in Table 1. The relatively detailed protocols including vector design, host cell line culture, transfection and selection of stable cell line as well as purification of rhNell-1 in HEK 293 and CHO system are described below, but are well known to those in the art.

TABLE 1 Mammalian Expression System for production of rhNell-1 Parental Leader Gene System vector sequence amplification CHO p3Xflag-CMV preprotrypsin No/optinal DXB11 mp19-Lp human tPA DHFR/MTX HEK293 pSecTag immunoglobulin No/optinal NS/0 or Sp2/0 pdCs-Fc-X light chain of Ig DHFR/MTX and Fc fragment pEE12 N/A GS/MSX DHFR: diydrofolate reductase; MTX: methotrxate; GS: glutamine synthetase MSX: methionine sulphoximine

A. Cho System #1

Vector design: A cDNA fragment was ligated into the expression vector p3×Flag-CMV (Sigma). The resulting expression construct, pCMV-rhNELL3×flag, includes a preprotrypsin leading sequence, cDNA fragment of the mature human NELL1 coding region and a 3×flag sequences at c-terminal.

Host Cell line: The CHO-K1 were adherent cell line and can be adapted to suspension culture in serum-free medium. The construct of pCMV-rhNell-1-3×flag was transfected by either lipofectamin (Invitrogen) or calcium phosphates treatment. The stable cell lines were selected by adding G418 (400-600 ug/ml) into the cell culture medium for about two weeks. The stable transformants were further screened for single clones with high productivity of rhNELL1 by limiting dilution. The selected stable cell lines can be expended in laboratory or industrial scale bioreactors for rhNell-1 production.

Purification procedure: rhNELL1 peptide containing media or cell lysate were purified through anti-flag antibody M2 (Sigma) affinity column at its native condition and eluted with 3×flag peptide.

B. Cho System #2

Vector design: FIG. 4A depicts the nucleic acid sequence of the cDNA construct and amino acid sequences of three different signal peptides that were used for the constructs.

Host Cell line: The CHO-K1 were adherent cell line and can be adapted to suspension culture in serum-free medium. The construct of pcDNA3.1-hNELL1-c-myc/His, pIL2-hNELL1-c-myc/His, or pN2-hNELL1-c-myc/His were transfected by either lipofectamin (Invitrogen) or calcium phosphates treatment. The stable cell lines were selected by adding G418 (400-600 ug/ml) into the cell culture medium for about two weeks. The stable transformants were further screened for single clones with high productivity of rhNELL1 by limiting dilution. The selected stable cell lines can be expended in laboratory or industrial scale bioreactors for rhNELL1 production.

Purification procedure: rhNELL1 peptide containing media or cell lysate were purified through immunoprecipitation through anti-c-myc agarose. FIG. 4B is a Western blot with anti-c-myc antibody detecting secreting NELL1 from transfections with different constructs after immunoprecipitation using anti-c-myc agarose. FIG. 4C is a Western blot with anti-c-myc or mouse anti-human NELL1 antibodies detecting secreting NELL1 after immunoprecipitation using rabbit anti-human Nell-1 antibody-NHS activated sepharose.

C. Cho System #3

Vector design: Proprietary cDNA constructs (from Aragnen Biosciences, Lonza, or Cytovance) using either NELL1 or NELL2 leader peptide sequences were constructed.

Host Cell line: The proprietary CHO cell lines were adherent cell line and can be adapted to suspension culture in serum-free medium. The proprietary constructs were transfected. The stable cell lines were selected by adding appropriate factors into the cell culture medium for about two weeks. The stable transformants were further screened for single clones with high productivity of rhNELL1 by limiting dilution. The selected stable cell lines can be expended in laboratory or industrial scale bioreactors for rhNELL1 production.

Purification procedure: rhNELL1 peptide containing media or cell lysate were purified through analytical and preparative protein purifications methods well known to those in the art (e.g., size, exclusion chromatography, ion exchange chromatography, affinity chromatography, immunoaffinity chromatography, high performance liquid chromatography,

Concentration procedure: rhNELL1 was concentrated using lyophilization or ultrafiltration.

D: HEK293 System

Vector Design: A cDNA fragment was ligated into the expression vector pSecTagA (Invitrogen). The resulting expression construct, pSec-hNell-1-Tag, includes a murine immunoglobulin κ-chain leader sequence, cDNA fragment of the mature human NELL1 coding region and dual tag of Myc and His sequences at c-terminal.

Host Cell line: The human embryo kidney cell line, HEK-293 which was adapted to serum-free medium and grown in suspension format, was transfected with the NELL1 peptide expression vector, pSec-hNell-1-Tag. Cells were either cultured for a couple of days as transient transfection before collecting conditioned medium for purification of rhNell-1 or treated with Zeocin (250 ug/ml) for selection of stable expression cell line. The stable transformants were further screened for single clones with high productivity of rhNell-1 by limiting dilution. The selected stable cell lines can be expended in laboratory or industrial scale bioreactors for rhNell-1 production.

Purification procedure: rhNell-1 peptide containing media were purified through Ni²⁺ affinity column at its native condition and eluted with 1M imidazole. The rhNell-1 was tested for its integrity, purity and bioactivity after extensively dialysis against at least 1000 volumes of PBS (pH 7.4) at 4° C. for 20 hrs.

In addition, the modifications of parental vectors for replacing existing leader sequence with a new one such as rat serum albumin, CD33, tPA and human interlukin-2 leader sequence or adding gene amplification target such as DHFR or GS into the backbone sequence will result in new expression vectors and systems. In this invention, the native signal peptide of human Nell-1 is not effective enough to guide the protein secretion and sometimes even the external leading sequence didn't work well, either. Thus, the construction of expression vector with in frame fusion of a small natural secretory protein such as human granulocyte-macrophage colony stimulating factor (GM-CSF) by a spacer containing intraprotein His tag and proteolytic cleavage site as “MPHHHHHHGGGDDDDKDPM” (SEQ ID NO:18) might be needed. The epitope tags used for purification of Nell-1 can be one of the following: 6× Histidines, 3×Flag, Myc, GST (glutathione S-transferase), EGFP or CTHS(C-terminal half of SUMO which stands for small ubiquitin modifying protein) etc, but also could be dual of His plus Myc as listed plasmid pSecTag in Table 1 (supra).

Furthermore, the dicistronic or multicistronic vectors using IRES might be constructed for regulatory or inducible expression of rhNell-1 under certain circumstances. The genetic modifications of host cell lines for gaining longer lasting proliferation and delayed apoptosis or compatible with special requests such as Tet (tetracycline) inducible system and Flp-In specific site integration system will be considered for improvement of rhNell-1 production.

Besides the stable expression of system for production of rhNell-1 mentioned above, we would not exclude the possibility to establish a large-scale transient transfection (LST) approach using multi-milligram purified plasmid vector (pREP4) to transfect HEK 293 or BHK suspension cells with cationic polymer PEI as backup alternative or complimentary to stable system.

Example 3 Purification of NELL2 Protein from Culture Medium

High Five cells carrying pIZT-FLC-NELL2 were cultured for about three days in serum free culture medium (1 L). The culture medium was centrifuged at. 3000×g for 5 minutes and the supernatant was collected. PMSF was added to a final concentration of 1 mM. Saturated ammonium sulfate solution (80% saturation (v/v) was added and the solution kept at 4 degrees for 1 hour. The solution was centrifuged at 15000×g for 30 min. and precipitate collected. Precipitate was dissolved in 50 ml of 20 mM Tris-HCl (pH 8.0), 1 mm EDTA at 4 degree and applied onto an anion-exchange chromatography UnoQ column (6 ml, Bio-Rad) equilibrated in 20 mM Tris-HCl (pH 8.0), 1 mM EDTA at 4 degree (1 ml/min speed by FPLC (Amersham-Pharmacia). The column was thoroughly washed with the same buffer.

The binding protein was then eluted by the gradation from 0 M to 1.5 M NaCl in the same buffer. The NELL2-FLAG fractions were identified by Western blotting using anti-Flag M2 (Sigma) Ab. The positive fractions were collected into one tube. Final product was dialyzed in the seamless cellulose tube (Wako, cutoff MW 12000) against 1 L PBS for overnight at 4 degree. The product was stored at −70 degree.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications can be made without departing from this invention in its broader aspects. Therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention. 

1. A composition for inducing bone or cartilage formation comprising: an effective amount of a recombinant Nel-like molecule-1 (NELL-1) peptide comprising an amino acid sequence of SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO:10, SEQ ID NO:12, and SEQ ID NO:14, and a carrier, wherein the carrier comprises a physiologically acceptable carrier that forms an implant or scaffold that provides for bone or cartilage formation.
 2. The composition of claim 1, wherein the NELL-1 peptide further comprises a NELL1 or NELL2 secretory peptide.
 3. The composition of claim 1, wherein the carrier is a scaffold.
 4. The composition of claim 1, which is in a formulation for injection into a fracture site or implantation.
 5. The composition of claim 1, further comprising another agent.
 6. The composition of claim 5, wherein the another agent is a selected from the group consisting of bone morphogenetic protein (BMP), a fibroblast growth factor (FGF), a transforming growth factor-β (TGF-β), an insulin-like growth factor (IGF), a vascular endothelial growth factor (VEGF), a platelet-derived growth factor (PDGF), a parathyroid hormone (PTH), a PTH-regulated protein) PTHrp), growth/differentiation factor 5 (GDF5); and LIM mineralization proteins (LMPs). 